Transparent will become translucent in time, polycarbonate is very tough and will resist shattering but it is not scratch resistant, anti scratch coatings exist for applications like helmet visors but they still suffer from marks. Acrylic wil shatter and is not scratch resistant so not recommended but it is much cheaper than polycarbonate.

Mike

PolyCarbonate is the way to go it can be shaped in a sheet metal folder Protect with thin cardboard sheet no heating required.

I have several for lathe and milling machine been in intermittent use for a number of years now.

Polycarbonate can be kept scratch free by occasionally removing the scratches with the likes of Brasso, obviously dependent on depth.

Martin P

No material is fool proof in guarding, you have to relate it to material size and velocity, then test it. I once saw a pit used to test turbines, the walls must have been a couple of feet thick going from steel to wood to a concrete liner. even with all the laminations blades were still embedded in the concrete. CNC machines tend to have multiple layered small windows, toughened glass, polycarbonate and steel mesh. I have seen a lathe guard where the part passed through and killed the operator. But as all say here polycarbonate of suitable thickness will prevent at least hot chips from hitting you, just don't get too close if turning something large at high speed and make it as big as possible.

Here's what happens when you expose acrylic (PMMA) to alcohol. I expect it's to do with residual stresses combined with the ability of alcohol to diffuse into acrylic. I expect it's liable to react to other hydrocarbons in a similar way. AFAIK, polycarbonate is much more stable / inert.

Funny timing – I'm trying to figure out the best approach to guarding my CNC machine myself, even as we speak. The table is long enough to lay someone out on, so full enclosure won't be possible by the time you allow for 700mm of movement. I'm thinking of some form of trick curtain at the ends to contain the coolant and chips. But a sliding / hinged polycarbonate front window / door seems sensible.

With a smaller machine like a Tormach, it's possible to fully enclose the entire machine. Threadexpress ("Cluff" Hall down under) has covered this extensively and thoughtfully on Youtube. Some interesting ideas there.

Murray

I made the mistake of cleaning masking tape marks off a £300 display case with meths

It was fine on the ordinary surfaces, but in the two spots where it got on cut edges – crazing.

Neil

Generally acrylic is more stable art organic fluids than PC, but, as shown, there are weaknesses. PC crazes and can shatter when contaminated with petrol, which is why I was surprised in its use for m/c helmets. I have an old PC one that I inspect closely on a regular basis, and will dump it as soon as the visor crazes.

However, in normal use for guards, PC is tougher.

Regards

Richard.